1. Field of the Invention
The present invention relates to a sound pick-up for frequencies in the range of audibility, particularly for musical instruments with resonant cavities, such as, string instruments. The sound pick-up includes a housing which can be fixed to the resonant body or cavity of the instrument and an induction coil or moving coil whose connections are conducted outside through the housing.
2. Description of the Related Art
Different embodiments of sound pick-ups have become known in the art. The sound pick-ups differ essentially from each other by the principal by which they operate. The known sound pick-ups operate in accordance with the piezoelectric principle, according to the electrostatic principle, or they are constructed as capacitor sound pick-ups. All of these sound pick-ups have in common that their dynamic properties are not properly balanced and they do not have a linear frequency pattern.
DE-OS 23 16 000 discloses a sound pick-up which includes a cylindrical housing in which an induction coil is mounted. This housing is mounted so as to be stationary relative to the musical instrument or the vibrating part thereof. A permanent magnet projecting into the induction coil is connected to the vibrating part of the musical instrument. Above the coil which is mounted stationary in the housing and separately from this coil is arranged a disk-shaped ferromagnetic body in an elastic, flat cushion, wherein the cushion surrounds the ferromagnetic body in its entirety and with play. This configuration of the sound pick-up is supposed to make it possible that only sounds emanating from the musical instrument are transmitted, but not sounds from the surrounding space, over the entire frequency range of the musical instrument. From the structural configuration of the known sound pick-up it is clear that it operates with forced excitation; in other words, the sound pick-up must be at rest relative to the musical instrument for producing a differential voltage.
The known sound pick-up has the following additional disadvantages. The known sound pick-up cannot be mounted in a freely vibrating manner. The vibrating behavior of the known sound pick-up is not sufficiently defined and it does not have any damping or only little damping. Because of the two vibrating parts, the resonant frequency must be expected in the middle range of audibility. For achieving useful voltages, the coil must be constructed with high impedance. The specification of DE-OS 23 16 000 even mentions the danger of humming. The musical instrument is strongly dampened by pressing the sound pick-up against a resting plane. For example, as shown in DE 23 16 000, a drum skin would be dampened very strongly. A free vibration is no longer ensured under these conditions. When the sound pick-up is mounted on a guitar, the vibrations of the strings are conducted through the elastic part of the sound pick-up before they can be transmitted through the sound pick-up housing and the screws onto the sound board. This significantly impairs the sound of a guitar and, depending on the type of guitar, may make the guitar useless.